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phylotypes, which were previously only detected in anoxic Black Sea sediments. In the same section of the core, the most abundant haptophyte sequence showed highest similarity with uncultivated haptophytes that were previously shown to grow mixotrophically as predators of picocyanobacteria, an adaptation that promotes growth in oligotrophic marine waters. Sequences with highest similarities to clones found in marine surface waters predominated in the S1 after ∼8 14 C kyr B.P. We discuss whether the shifts in haptophyte and dinoflagellate populations inferred from the preserved DNA reflect known environmental changes that occurred during the formation of sapropel S1.

[1] High-resolution laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) scanning of laminated sediments from the Urania basin is used to investigate short-time-scale variability in export productivity and redox conditions during the formation of eastern Mediterranean sapropel S1. Sedimentary enrichments of molybdenum (Mo), vanadium (V), and uranium (U) reflect deep-water redox conditions, most likely those near to the seawater-brine interface, while enrichment of Ba is related to biogenic barite and hence to export productivity. The enrichments of all four elements show strong variability on multidecadal to multicentennial time scales throughout S1. A partial decoupling of export productivity from redox conditions at the height of sapropel formation suggests that hydrographic changes, i.e., a variable ventilation rate of the eastern Mediterranean, played an important role in determining deep-water redox conditions. A pronounced switch is observed in the enrichments of redox-sensitive trace metals, from dominantly 300–600 year variability during early S1 to dominantly 100–300 year variability during late S1, indicating a change in the mean frequency of variability in the ventilation rate. The presence of a similar shift in the frequency of tropical and extratropical climate records at this time suggests that ventilation of the eastern Mediterranean was coupled to global climate variability.

[1] XRF sediment core scanning technology is increasingly used to quantify sediment composition. The overall good correlation between biophilic halogen bromine (Br) and sedimentary total organic carbon (TOC) potentially allows the fast estimation of down core TOC profiles by XRF scanning. In order to test this approach we present data from the Arabian Sea and a Mediterranean brine basin, comparing XRF core scanning Br data with discrete sample TOC analyses. Overall, Br counts and TOC show a clear correlation, except when stable carbon isotope and C/N data indicate intervals characterized by enhanced input of terrestrial organic matter. Hence, solid phase Br is exclusively associated with marine organic matter (MOC) and can be used as a direct estimate of this parameter after a calibration is established. High pore water Br in the brine core steepens the Br/TOC correlation but after salt correction shows a nearly identical gradient to that of the Arabian Sea core.

[1] The residual dark unit of the most recent eastern Mediterranean sapropel (S1) is usually overlain by sediments with enhanced concentrations of MnOx in two separated layers. The variability and magnitude of the Mn enrichment at different locations and water depths indicate that Mn must have been added preferentially to sediments at intermediate (1–2 km) water depths. We propose a two-stage mechanism for the Mn enrichment that involves decreasing oxygenation with increasing water depth. This mechanism involves the loss of reduced Mn2+ from the deepest sediments (>2 km water depth) into overlying anoxic waters and a variable gain of MnOx in sediments in contact with oxygenated waters at shallower depth. In the S1 unit that receives the extra MnOx input, an upper higher Mn-enriched zone (>3 wt %) is maintained continuously at the top of the accumulating S1 unit because the pore waters are anoxic at shallow sediment depth while bottom waters are oxic to some degree. In a reactive-transport model, the Mn enrichment in the upper zone could not be supported by normal sediment diagenesis. Thus the MnOx in the upper Mn horizon must have formed mainly in the water column. The MnOx in the upper Mn-enriched zone adsorbed Mo and Li from seawater in a similar manner as other Mn-enriched oxic sediments, nodules, and crusts, with a Mn:Mo ratio of ∼600:1, a Mn:Li ratio of ∼750:1, and a δ98/95MoMOMO of −2.5 ‰.